The demands on communications systems are increasing at a tremendous rate. Reliable data transfer at the rates required for applications such as signal processing necessitate the use of optical communications. As these systems become sufficiently complex, the use of optoelectronic integrated circuits (OEIC) is becoming increasingly attractive for cost and performance reasons. In the last several years, significant efforts have been made toward the monolithic integration of devices formed of III-V compounds and alloys thereof and in particular GaAs electronic and GaAs/GaAlAs optical devices on GaAs wafers. These efforts to date have been successful from the standpoint of preliminary concept demonstration but have been limited by the immaturity of GaAs electronic device technology and the quality of the GaAs material itself. Recent progress in obtaining high-quality GaAs on Si substrates offers the potential to overcome these obstacles. The key advantage of GaAs on Si for integrated optoelectronic components is that the electronic circuits can be fabricated in Si wafers. The design and fabrication technology of Si circuits is well developed and the economics of such circuits are also very attractive. This approach to monolithic GaAs and Si integration will complement Si circuits with GaAs/GaAlAs optical components.
The essence of monolithic integration technology is not only the ability to grow high-quality GaAs on Si substrates but also the ability to fabricate GaAs and Si devices together on a single chip. The ability to grow high quality GaAs layers on Si substrates has been demonstrated by several groups. The fabrication of GaAs and Si devices together on one chip has also been demonstrated.
Full monolithic integration of interconnected GaAs/GaAlAs double heterostructure LEDs and Si MOSFETs has also been demonstrated (see copending U.S. Pat. application Ser. No. 874,295 now U.S. Pat. No. 4,774,205 incorporated herein by reference). The Si MOSFETs, with a gate length of 5 um and a gate width of 1.6 um, have essentially the same characteristics as those of control Si MOSFETs fabricated on a separate Si wafer. An LED modulation rate of 27 Mbit/sec, limited mainly by the speed of the Si MOSFET, has been demonstrated by applying a stream of voltage pulses to the MOSFET gate.
While their performance is good, optoelectronic devices fabricated on GaAs on Si, including solar cells, LEDs, and diode lasers, have not yet reached the quality of those fabricated using GaAs substrates. As the material quality of GaAs on Si improves to where defect densities are lower than 10.sup.5 cm.sup.-2, the performance of LEDs should be similar to LEDs on GaAs substrates. The performance of lasers will also be similar when the dislocation densities reach 10.sup.3 to 10.sup.4 cm.sup.-2.